Optical assembly for use in a skin treatment device

This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2022/065651, filed on Jun. 9, 2022, which claims the benefit of European Patent Application No. 21180439.8, filed on Jun. 18, 2021. These applications are hereby incorporated by reference herein.

The invention relates to an optical assembly for use in a skin treatment device, preferably, a photoepilation device, more preferably, an intense pulsed light-based device. The invention further relates to the device comprising the optical assembly, and a method of using the assembly in the device.

Pulsed light can be used for performing hair or skin treatment such as cosmetic hair removal. The light pulse is generated using sources such as lamps, light bulbs, light emitting diodes or lasers. It penetrates the skin and is absorbed, e.g. in the root of the hair. The temperature of the root of the hair consequently rises. The growth of the hair is inhibited if the temperature rise is sufficiently high. This process is known as selective photothermolysis.

Light-based treatment devices, such as intense pulsed light (IPL) devices, photo epilation devices, skin rejuvenation devices, phototherapy devices or pain relief devices, often use incoherent light for skin or hair treatment. For example, IPL technology uses light from e.g. a halogen, e.g. Xe, flash lamp at a relatively low fluence (up to 6.5 J/cm2) (as compared to professional devices, for permanent photoepilation, that use fluences in excess of 10 J/cm2), and relatively high beam divergence (e.g. compared to lasers).

EP 3 281 598 A1 discloses a laser skin treatment device for laser induced optical breakdown of hair or skin tissue. A beam scanning system scans the beam using a rotated prism which implements a lateral shift to the beam. A focusing system at the output side of the beam scanning system focuses the incident light beam into a focal spot in the tissue.

In contrast to treatment devices where optical fibers are used as waveguides to guide light to a target (skin), in devices using prism-based light waveguides, the treatment light needs to be bent at relatively large angles (e.g. 90 degrees) to be guided effectively to the skin. The inventors of the present invention have recognized that it is not always possible to achieve such guidance in the latter. For example, as shown in, light rays may bypass reflection at the prism, so that they are incident at incorrect angles in the waveguide. Moreover, since some rays are reflected and others not, there is a non-uniform angular and spatial distribution of the light beam/treatment light in the device. Such rays are not effectively directed to the target. Furthermore, due to the incoherent light source characteristics of the device, the emitted light is diffuse and characterized by a wide range of propagation angles. It is an object of the invention to provide an optical assembly to effectively guide such diffuse light using a prism-based optical waveguide, ensure uniformity of the treatment light, and in turn improve device treatment efficiency. It is a further object of the invention to reduce light leakage while guiding the light through the waveguide.

Another problem, as shown in, is that while using prism-based waveguides, even after undergoing reflection in the prism, some incident light/rays may be redirected towards the treatment source. This may happen when light rays are incident on a sub-optimal position on the reflective surface of the prism, e.g. on an upper part of the prism hypotenuse. It is another object of the invention to provide an optical assembly which increases the flux of incident light directed towards the target by reducing such back propagation of light.

Additionally, prior to treatment, it is desirable to obtain characteristics (e.g. pigmentation) of the skin/target positioned adjacent to a device treatment aperture via which the treatment light pulses are applied to the skin. Other aspects like detection of skin contact, hair count or displacement and motion of the device are equally desirable. For example, if no skin contact or an unsafe skin tone is detected, the device is prevented from flashing. It is yet another object of the invention to provide an optical assembly which facilitates incorporation of further optical elements which can carry out these functions. According to an aspect, an optical assembly for use in a skin treatment device is provided. The optical assembly comprises a light source, a first prism and first and second guiding elements with bound/enclosed reflective faces disposed opposite to or facing each other. The first prism includes a first surface, a second surface inclined with the first surface and a third surface adjoining the first and the second surfaces. The first guiding element is arranged to guide the light transmitted from the light source through the first surface of the first prism to its third surface. The second guiding element is further arranged to receive through the second surface of the first prism, the light reflected from the third surface of the first prism and output the received light for illuminating a target/body part (skin). The first surface and the second surface of the first prism are separated from the first guiding element and the second guiding element, respectively, by a refractive index interface. In other words, there exists a material which is different from the prism material, in contact with each of the first surface and the second surface. The first and second surfaces are total internal reflection surfaces. According to another aspect, a method is provided for performing a cosmetic or non-therapeutic treatment of the target using the optical assembly.

According to an aspect, the third surface of the first prism or a surface of the second guiding element is coated, at least partially, with a reflective coating e.g. on an outer side. According to an aspect, the first prism and/or the first light guiding element and/or the second light guiding element is a total internal reflection (TIR) guiding element. When the first prism acts as a TIR element, the first and/or second surfaces of the first prism are disposed in contact with a medium (e.g. the material of the adjacent guiding element) of a refractive index less than a refractive index nof the first prism.

The third surface of the first prism may further be in contact with a medium of lower refractive index (air or a reflective coating). When the first or the second guiding element acts as a TIR element, the reflective faces of the first light guiding element and/or the reflective faces of the second guiding element are disposed in contact with air (medium of lower refractive index).

According to an aspect, a light exit face of the first guiding element and/or a light entry face of the second guiding element are separated by a predetermined gap from the first surface of the first prism and the second surface of the first prism, respectively. The gap further comprises a dielectric material, wherein the dielectric material has a lower refractive index than a refractive index of the first prism. The gap may further comprise metallic, glass and/or ceramic particles.

According to an aspect, the optical assembly further comprises a second prism having a first surface and second surface inclined with each other and a third surface adjoining the first and the second surfaces, wherein the third surface of the second prism is removably attached or fused to a portion of the third surface of the first prism or a reflective surface of the second guiding element, and such that the first surface of the second prism is disposed substantially parallel to the second surface of the first prism. The second surface of the second prism may comprise a reflective coating, e.g. on its outer side. The third surface of the second prism may further include a deformable layer such as a transparent silicone layer. The second surface of the second prism may be connected to a movable actuator.

According to an aspect, the optical assembly further comprises an imaging element for imaging the target through the first surface of the second prism. The imaging element may be mounted on the first surface or another suitable component of the optical assembly for this purpose.

According to an aspect, there is provided a light filter and/or an insulating window in the optical assembly. A cooling member is further provided in thermal contact with the first prism.

According to an aspect, a device comprising the above-mentioned optical assembly is provided, which is suitable for treating a body part/skin of a user. According to an aspect, the second guiding element is disposed in a removable attachment of the device.

According to an aspect, a computer-implemented method for performing cosmetic or non-therapeutic treatment of skin is provided. The method comprises providing an optical assembly as mentioned, determining, based on at least one image obtained by an imaging element of the optical assembly whether or not to perform the treatment, and if yes, guiding light emitted by a light source of the optical assembly to the target for performing the treatment.

These and other aspects, and further advantages, will be apparent from and elucidated with reference to the embodiment(s) described herein.

The matters exemplified in this description are provided to assist in a comprehensive understanding of various exemplary embodiments of the present invention disclosed with reference to the accompanying figures.

Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the exemplary embodiments described herein can be made without departing from the scope of the claimed invention. In particular, combinations of specific features of various aspects of the invention may be made. An aspect or embodiment of the invention may be further advantageously enhanced by adding a feature that was described in relation to another aspect or embodiment of the invention.

Further, the functionality associated with any particular means may be centralized or distributed, whether locally or remotely. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. It may be advantageous to set forth that the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. In addition, reference to an element by the indefinite article “a” or “an” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article “a” or “an” thus usually means “at least one”.

The expression “at least one of A, B and C” means “A, B, and/or C”, and that it suffices if e.g. only B is present. Any reference signs in the claims should not be construed as limiting the scope.

A surface is defined herein to refer to the faces of various optical components. The skilled person imparts the same meaning to these terminologies.

The light emitted by a light source (one or more) for treatment purposes is referred to as “treatment light”. The light-based treatment device may comprise further light sources for emitting light that is not used as treatment light.

Although the method may be intended towards cosmetic treatment, the use of the device for medical treatments is not excluded herein. Further, although the method may be performed at home, it goes without saying that the method may also be practically exploited in an industrial setting, for example, in commercial salons.

The term “user” used herein may be used to refer also to the person using the device, and not necessarily the target whose skin is treated.

The term “guiding element” encompasses any element having sufficient dimensions (length, width or height equal to or different from one another) which can guide light. These elements may be elongated, and have shapes such as rectangular, square, triangular (e.g. a prism), trapezoid, planar, curved or a hybrid of planar and curved (e.g. plano-concave) and the like. Guiding elementsandmay further comprise fully or partially bound surfaces (faces).

show top cross-sectional views of optical arrangementaccording to an exemplary embodiment of the invention. The arrangement can be positioned inside a skin or hair treatment device, such as the IPL device.

The optical arrangementcomprises light sourcewhich can generate light for illuminating and thus treating target. The light sourcecan generate light pulses of any suitable or desired wavelength (or range of wavelengths) and/or intensities. For example, the light sourcecan generate visible light, infra-red (IR) light and/or ultraviolet (UV) light. In an embodiment, the arrangement comprises multiple light sources. Each light sourcecan comprise any suitable type of light source, such as one or more light emitting diodes (LEDs), a (Xenon) flash lamp, one or more lasers (e.g. laser diodes, VCSELs), etc. The light source(s)can provide light pulses with spectral content in the 530-1200 nanometre (nm) range for a duration of around 2.5 milliseconds (ms), as these wavelengths heat melanin in the hair and hair root by absorption, which puts the hair follicles in a resting phase, preventing hair regrowth. These wavelengths further enable a contrast in absorption between the hair and surrounding dermis and ensure that light is minimally absorbed by the latter. In an embodiment, light sourceis a broadband light source which emits light in a broad spectrum of wavelengths or frequencies.

The optical arrangement further comprises a prism (first prism) which is arranged to receive the light emitted from the light source. First prismcomprises a first surface, a second surfaceinclined with the first surfaceand a third surfaceadjoining the firstand the secondsurfaces. The geometry of a prism, e.g. that the prism includes more surfaces than those exemplified in the drawings, is well-known to those skilled in the art. In an embodiment, the first surfaceand the second surfacemay be two orthogonal surfaces of a right-angled prism, preferably, a right-angled isosceles prism, and the third surface, the oblique surface (hypotenuse) which connects the orthogonal first surfaceand the second surface. This prism configuration results in a light path which is bent by 90 degrees, i.e. the angle between the first surfaceand the second surface. Other prism configurations result in light bending angles corresponding to the angle between their respective first surfaceand the second surface. First prismmay be made of material with a suitable refractive index n.

Guiding elementsandare further illustrated inas part of the optical assembly.

For example, guiding elementmay comprise surfaces,,and, where surfacesandface each other on opposite sides of the first guiding element, e.g. on opposite sides of an axis L through the light source, the first guiding elementand the first prism. Surfacesandface each other on another two opposite sides of the guiding elementand extend perpendicular to said axis. Surfacesandare further bound (closed) surfaces. Hence, surfacesandenclose the guiding elementfrom opposite directions. Surfaces,,andmay be regarded as top, bottom and two side surfaces of the first guiding elementherein.

The first guiding elementis disposed between the light source and the first prismsuch that the light emitted from the light sourceis guided therethrough to the first surfaceof the first prism. Air may be present as medium between light sourceand the first guiding element, so that the light emitted from the light sourcetravels through air (refractive index n=1) to the first guiding element. Opposite facing side surfaces/facesandact as light entry and light exit faces, respectively, for light emitted from the light source. Edgeseparating top surfaceand side surfaceof the first guiding elementmay be positioned to be flush with edgeseparating first surfaceand third surfaceof the first prism. Edgeseparating bottom surfaceand side surfaceof the first guiding elementmay be positioned to be flush with edgeseparating first surfaceand second surfaceof the first prism.

Similarly, bound surfacesandface each other on opposite sides of the second guiding elemente.g. on opposite sides of an axis L′ through the second guiding elementand the first prism. Hence, surfacesandenclose the guiding elementfrom opposite directions. The second guiding elementis arranged to receive, through the second surfaceof the first prism, the light reflected from the third surfaceof the first prism and output it for illuminating and thereby treating the target(body part e.g. skin or hair, of a user). Light incident on bound surfacesandis reflected by these surfaces towards the treatment aperture. Depending on the dimensions of the first guiding elementand the second guiding element, multiple reflections may occur at,and,. Such reflections are not excluded herein.

In the embodiment of/, opposite facing surfacesandwhich extend perpendicular to axis L′ act as light entry and light exit faces, respectively, for light reflected from the third surfaceof the first prism. Surfaces,,andmay be regarded as side, top and bottom surfaces of the second guiding elementherein. In an embodiment, e.g. as shown in, surfacesandmay simply face each other at an inclination, i.e. without being parallel to each other. In this case, surfacemay bisect axis L′ and be adjoined to surfacewhich is parallel to axis L′. Surfacemay connect surfacesand, so that the second guiding elementtakes the shape of a prism. Hence, it is not essential for guiding elementto comprise surface. Here, surfaceacts as the light exit face, as shown in.

Edgeseparating side surfaceand top surfaceof the second guiding elementmay be positioned to be flush with edgeseparating first surfaceand second surfaceof the first prism. Edgeseparating side surfaceand top surfaceof the second guiding elementmay be positioned to be flush with edgeseparating second surfaceand third surfaceof the first prism.

As a result of bound top and bottom surfacesandof guiding elementand side surfacesandof guiding element, both the treatment light emitted from light source, and that reflected from the third surfaceof the first prismare confined to the interior of the respective guiding element, reducing losses due to beam divergence. This in turn increases the amount of light flux incident on the target. The bound surfaces of guiding elementsandare further reflective (e.g. made of metal, glass), so that any diverging treatment light is reflected by the bound surfaces and (re)-guided towards the first surfaceof the first prismor towards the treatment aperture to target, further increasing the amount of light flux incident on the target.

The multi-element (therefore including multiple refractive interfaces) optical assembly comprising the first prism(e.g. a solid prism), the first guiding elementand the second guiding elementcreates refractive index variations/differences at surfacesandof the first prism. Light rays,,andare shown for illustration purposes in. Each light ray transmitted from light sourceenters the first prismthrough first surface(where it is refracted) and is reflected by third surface, before passing the second surfaceof the first prism(where it is refracted again) towards the target. Light raymay further be indirectly incident on the third surfacevia reflection at second surface. In an embodiment described below, this reflection may arise from TIR at the second surface. After reflection at the third surface, light raymay further reach second surfaceindirectly via reflection at the first surface. In an embodiment described below, this reflection may arise from TIR at the first surface. Because the rays entering the first prismthrough first surfaceare reflected by the third surfaceand transmitted through the first prismvia the second surface, light leakage in the optical assemblyis reduced. Consequently, the flux of incident light directed towards the targetis increased. Due to said optical path of the treatment light, spatial and/or angular uniformity is further maintained.

In an embodiment, third surfaceof the first prismfurther includes a reflective coating R, so that treatment light which is incident on the third surface suffers minimal transmission losses while being reflected by the surface.

The first guiding elementand the first prismmay be disposed in contact (and hence edges,and edges,are both flush and in contact with each other), as shown in, or be disposed at a separation from one another as shown in. Similarly, the second guiding elementand the first prismmay be disposed in contact (and hence edges,and edges,are both flush and in contact with each other), or be disposed at a separation from one another.

In an embodiment, side surfacesandof first guiding element, and top and bottom surfaces,of second guiding elementmay further be open or closed.

With open side surfaces/facesand, first guiding elementis essentially a hollow guiding element/waveguide so that the first surfaceis disposed in contact with air (any fluid) as medium separating the first prismand the light source. Similarly, with open top and bottom surfaces,, second guiding elementis essentially a hollow guiding element so that the second surfaceis disposed in contact with air (fluid) as the medium separating the first prism and the treatment aperture of the device. Treatment light may still be confined between the bound surfaces of the first and the second guiding elementsandas indicated. The hollow guiding element allows for an optical assemblywith reduced weight, and thus making a deviceincorporating the optical assemblylighter. In practical implementations, such a hollow guiding element may be a pipe with reflective inner surfaces. These surfaces typically comprise a metallic layer (e.g. a layer which is deposited on a transparent substrate or a metallic foil by vacuum techniques).

Alternately, the first guiding elementand second guiding elementmay be a hollow element with closed/bound side surfaces/faces,of first guiding element, and bound top and bottom surfaces,of second guiding element. In an implementation, such a guiding element may be a a closed pipe with reflective surfaces. In this case, for example, side surfaceof first guiding elementand top surfaceof second guiding elementmay be disposed at a distance from the first surfaceand the second surfaceof the first prism, respectively.

With closed/bound side surfaces,of first guiding element, and bound top and bottom surfaces,of second guiding element, first guiding elementand second guiding elementmay be a solid with appropriate refractive indices nand n, where nis the same as or different from n. The refractive indices n, nof the first and the second guiding elements,, and nof the first prismmay be further chosen to allow total internal reflection of light (TIR) within the first guiding elements, the second guiding elementand the first prism, to further minimize transmission losses (light leakage) in the optical assembly. Preferably, the solid guiding element may be made of transparent material with a sufficiently high refractive index to guide the angular distribution of the beam generated by the light source.

TIR occurs when a light ray(or-) propagating in the first guiding elementmade of a material e.g. a solid with certain refractive index (e.g. glass, n=1.5) strikes top surfaceor bottom surfacewhich acts as boundary between the solid with higher refractive index and air having a lower refractive index (n=1) (said surfaces are disposed to be in contact with air) at an angle larger than a critical angle θ(measured with respect to an axis/normal extending perpendicular to the topor bottomsurface of the first guiding element). In this case, the light ray is entirely reflected at surfacesand. As a result of TIR, light transmission losses at the reflective surfaces of the first guiding elementare further reduced.

TIR may further occur when the light raypropagating in the first prism made of a solid (e.g. glass, n=1.5) strikes surface,orwhich acts as boundary between the solid with higher refractive index and a medium (e.g. air, resin, solid) having a lower refractive index at an angle larger than a critical angle θc (measured with respect to an axis/normal extending perpendicular to the respective surface of the first prism). In this case, the light ray is entirely reflected at surfaces,and.

In an embodiment, the refractive index nof the first guiding elementmay be less than refractive index nof the first prism, to satisfy the above-mentioned TIR condition.

Assuming a raywhich is reflected by third surfaceof the first prismis incident on the first surfaceof the first prismand satisfies TIR condition, this light ray is total internally reflected at first surfaceand hence coupled back to the prism towards the treatment aperture. This reduces instances when a ray, after reflection by the third surface, leaks out of the first prisminto the first guiding elementthrough first surface. As a result of TIR at first surface, such light is redirected to surfacewhich either transmits the light further or reflects it to surfacedepending on the angle of incidence of such light. Further, when guided towards the first prism, the light ray,,oris not total internally reflected at the surface

The arrangement therefore reduces back coupling of the light to the first guiding element in a direction towards the treatment source, and in turn improves the uniformity of the treatment light and increases the amount of light directed to the skin.

In another embodiment, the refractive index nof the second guiding elementmay be less than refractive index nof the first prism.

Assuming a raywhich originates from first surfaceof the first prismis incident on the second surfaceof the first prismand satisfies TIR condition, this light ray () is total internally reflected at second surfaceto the third surfaceof the first prism, which can then be further reflected by the third surface.